1. Field of the Invention
The present invention relates to a permanent-magnet generator for producing electric power by virtue of electromagnetic induction caused by relative movement of magnets and electricity-generating coils due to rotation of a flywheel.
2. Description of the Background Art
As an example, a conventionally known permanent-magnet generator is configured such that a plurality of air passages are formed in a bottom portion of a generally cup-shaped flywheel with fins projecting inward from an outer ringlike portion of the flywheel, each fin being located between one air passage and another, to achieve an improved ventilating efficiency inside the flywheel. This kind of permanent-magnet generator is found in Japanese Patent Application Publication No. 2002-101630, for example. When the permanent-magnet generator is in operation, the fins rotate together with the flywheel, creating negative pressure around each air passage, whereby fresh outside air is introduced into the generator to replace inside air.
As in the aforementioned example of the prior art, conventional permanent-magnet generators are often provided with fins for introducing outside air and discharging inside air through air passages from an internal space of a flywheel. If a one-way clutch or the like is fitted to the bottom portion of the flywheel, however, part or all of the air passages might be blocked, leading to a problem that the interior of the permanent-magnet generator is not well ventilated with the aid of the air passages. Should such a situation occur, heat which builds up inside the generator will not be dissipated enough because the fins provided in the conventional permanent-magnet generator can not sufficiently stir up hot inside air.
In addition, as a result of recent tendency, toward higher output power of permanent-magnet generators and a higher frequency due to an increase in the number of magnetic poles produced by magnets and a core, temperature produced by heat buildup in electricity-generating coils is increasing. This temperature increase develops such problems as a decrease in service life and reliability of insulating coating and deterioration of generator efficiency. Under such circumstances, there is a growing demand for a permanent-magnet generator which can ventilate an internal space of a flywheel.